In offices the world over, heaps of printouts and photocopies from laser printers get used once before being discarded, or tossed on shelves to collect dust indefinitely. But what if they could be wiped clean and used again?
An engineering team at the University of Cambridge in the UK has figured out how to erase pages by vaporising common toners using a laser-based technique that doesn't damage the underlying paper. It can delete words and images printed on paper.
Toshiba of Japan already sells a special laser printer/copier (video) that uses a blue toner which can be almost completely erased with heat treatment. David Leal-Ayala and his colleagues at Cambridge have taken the idea a step further, though, with a method that can recover the paper from any laser printed or photocopied document. After testing and ruling out toner removal processes that use mechanical abrasion and chemical solvents, they focused on the most promising method: laser pulses which vaporise toner particles in thin layers until they are no more.
"The key idea was to find a laser energy level that is high enough to ablate - or vaporise - the toner that at the same time is lower than the destruction threshold of the paper substrate. It turns out the best wavelength is 532 nanometres - that's green visible light - with a pulse length of 4 nanoseconds, which is quite long,"Leal-Ayala.
Allwood and colleagues estimate it would cost Rs. 1,330,000/- to build a prototype unprinter but that the costs would come down as technology improves and it is commercialized. They believe that reducing the cost would make the device valuable in most offices by reducing the need to buy paper. It could also be kinder to the environment by reducing the need to use as many chemicals to recycle paper and cutting carbon emissions savings of up to 79 percent, they noted.